As an example of a transmission system in which contents data is transmitted or received between a plurality of transmission terminals through relay devices, there is a video conference system in which a video conference takes place via a communication network such as the Internet. Recently, the need for a video conference system is growing because of a tendency of saving expenses and time for business trips. In the video conference system, a plurality of video conference terminals are used as an example of the transmission terminals. The video conference can be made by reception and transmission of image data and voice data between the video conference terminals.
Further, the recent enhancement of the broadband environment made it possible to transmit and receive high-quality image data and high-quality voice data. Thus, a situation of the other party of the video conference is easily recognized, which leads to improved fidelity of communication.
However, when a large number of video conferences are conducted via the communication network or when the image data or the voice data is received through the narrowband channel on the communication network, the image data or the voice data may be delayed. If the image data or the voice data is delayed by 0.5 seconds or more, it is reported that the user of the video conference feels stress during the conversation. Thus, in spite of the recent enhancement of the broadband environment, it happens sometimes that the user cannot perform the satisfactory video conference.
In recent years, in connection with the video conference system, relay devices that relay the image data and the voice data between the video conference terminals are installed for every local area network (LAN) in the communication network. When the video conference communication process is performed in distributed manner through these relay devices, a load on each relay device can be reduced and a data transmission amount of the image data or the voice data to be relayed can be distributed.
Conventionally, in selecting and using one relay device from among a plurality of relay devices, a relay device on the same LAN as the video conference terminal that participates in the video conference, was used. That is, by selecting a relay device having an IP address close to an IP address of the video conference terminal, transmission and reception of the high-quality image data is enabled through the selected relay device (see Japanese Patent Application Laid-open No. 2008-227577).
However, in the conventional video conference system, the relay device is selected under the presumption that the high-quality image data or the high-quality voice data can be transmitted and received if the relay device having the IP address close to the IP address of the video conference terminal is used. Thus, it may not well-suited for the actual communication network environment. For example, even if the IP address of the video conference terminal and the IP address of the relay device are obtained in advance, since it is difficult to grasp access states of all communication networks in the world, the presumption is not always correct. For example, there may be disconnections in actual environment. Therefore, it is difficult to transmit and receive the image data or the voice data of as high quality as possible under the actual communication network environment.